Telecommunication systems using light propagating in different waveguides expand more and more today. There is a large interest in extending the optical networks even up to private homes or local business estates, the so called local access network which is also called "Fibre To (In/From) the Home", "Fibre To (In/From) the Customer (Business)", etc. Also, there is a large interest in extending the use of optical networks in LANs, i.e. local area networks, used for interconnecting computers in a business estate and furthermore for communication inside computer equipment and for communication between computers and peripheral devices such as printers etc. In order to achieve this expansion, the costs of the components of the optical networks of course have to be reduced as much as possible. Very important costs are related to producing the optical transmitter and receiver modules including lasers, LEDs, etc. and other active or passive devices. A part of these costs are in turn associated with testing finished optoelectrical modules which are to be mounted e.g. on printed circuit boards.
In conventional testing of optical modules manufactured at the surface of a substrate the respective optical device of a module is energized and the light is emitted in the case of an optical transmitter device and the electrical signals output from an optical receiver device are studied when injecting light into the receiver device. Such a method is disclosed in e.g. U.S. Pat. No. 5,631,571. General testing methods of electro-optic modules are disclosed in U.S. Pat. Nos. 5,631,759 and 5,546,325 and microlenses for injecting light for such testing is described in Tsai, Yang and Le, "A novel scheme for efficient excitation of high-density channel-waveguide array using ion-milled planar microlens array", Optoelectronics, Devices and Technologies, Vol. 5, No. 2, December 1990, pp. 317-324.